1. Field of the Invention
This invention relates to an improvement in inflators that are designed to lower internal pressure capability in order to minimize weight such as inflators that utilize aluminum in place of steel in the construction of the casing or housing.
2. Description of the Prior Art
Many forms of inflators for the inflation of inflatable crash protection or "air bag" restraint systems are known in the prior art. One form of such inflators utilizes a solid fuel gas generant composition for the generation of the inflating gas and includes as main component parts an annular reaction or combustion chamber which is bounded by inner and outer casing or housing structures, as disclosed, for example, in U.S. Pat. No. 4,296,084, granted to G. V. Adams and F. E. Schneiter and assigned to the assignee of the present invention.
Such gas generators or inflators must be constructed to withstand enormous thermal and mechanical stresses for a short period during the gas generation process. Thus, inflators that have been and are currently being used to fill automobile or other vehicle crash bags are fabricated using steel for the casing and other housing structural components, with the structural components being joined together by screw threads, roll crimping or welding.
Recent emphasis on weight reduction in automobiles has created a need for a lighter weight crash bag inflation system. It has been determined that significant weight reduction in the inflator can be achieved by the utilization of aluminum for the steel housing and other structural components. A form of inflator that utilizes aluminum for the housing structure is disclosed and claimed in the copending application entitled "INTERTIA WELDED INFLATOR" bearing Ser. No. 595,774, filed on April 2, 1984 by Wilbur J. Ahlf, Gary V. Adams, Donald J. Cunningham and Daniel P. Dahle. That application is assigned to the assignee of the present invention. The disclosure thereof, by reference, is incorporated herein.
The housing construction of the Ahlf et al. "INERTIA WELDED INFLATOR" includes first and second aluminum structural components, specifically, a diffuser shell and a base shell. The diffuser shell and the base shell are welded together in a single inertia welding operation to form igniter, combustion and filtering chambers, the assembly being welded in a wholly loaded condition.
A problem is encountered when inflators utilizing aluminum for the housing construction are subjected to a high temperature environment such as a bonfire. This problem stems from the fact that at a temperature in the 650.degree. F. (343.degree. C.) range the pyrotechnics of the inflator automatically ignite. In this temperature range, for convenience termed the "auto ignite" temperature, the aluminum of the housing structure degrades and tends to rupture or burst, sending pieces and fragments flying in all directions. This problem is not encountered with inflators that employ steel in the housing structure since steel does not degrade until a much higher temperature of about 1100.degree. F. (593.degree. C.) is reached. The use of aluminum in an inflator, in place of steel to minimize weight, thus results in a lower inflator internal pressure capability. This lower internal pressure capability could be hazardous in a high temperature environment such as the inflator might be subjected to in the event of fire whether in storage, being shipped, or installed in a vehicle.
Thus, there is a need and a demand in such inflators that have housing structures that are designed to a lower internal pressure capability in order to minimize weight for a solution to this problem.